bug(windows): automatic updates may not be able to find downloaded packages when admin user is not same as current user

`Kmshell -ikp` is called, but does not pass any information about downloaded files. The admin user may not even have access to the files for the current user. So we need to consider, in this scenario, how to download and make the files accessible to the admin user.

https://github.com/keymanapp/keyman/blob/9c7b1a6ae6ddedbceff48ecb37a805e591abcaee/windows/src/desktop/kmshell/main/Keyman.System.UpdateStateMachine.pas#L1209-L1240

See also #16162, as this will also need to handle passing the baselayout setting to the elevated process.